The crystal structure of the dimeric PvuII restriction endonuclease (R.PvuII) has been determined at a resolution of 2.4A. The protein has a mixed alpha/beta architecture and consists of two subdomains. Despite a lack of sequence homology, extensive structural similarities exist between one R.PvuII subdomain and the DNA-binding subdomain of EcoRV endonuclease (R.EcoRV); the dimerization subdomains are unrelated. Within the similar domains, flexible segments of R.PvuII are topologically equivalent to the DNA-binding turns of R.EcoRV; potential catalytic residues can be deduced from the structural similarities to R.EcoRV. Conformational flexibility is important for the interaction with DNA. A possible classification of endonuclease structures on the basis of the positions of the scissile phosphates is discussed.

The crystal structures of bovine pancreatic ribonuclease A (RNase A) in complex with 3Ј,5Ј-ADP, 2Ј,5Ј-ADP, 5Ј-ADP, U-2Ј-p and U-3Ј-p have been determined at high resolution. The structures reveal that each inhibitor binds differently in the RNase A active site by anchoring a phosphate group in subsite P 1 . The most potent inhibitor of all five, 5Ј-ADP (K i ‫ס‬ 1.2 M), adopts a syn conformation (in contrast to 3Ј,5Ј-ADP and 2Ј,5Ј-ADP, which adopt an anti), and it is the ␤-rather than the ␣-phosphate group that binds to P 1 . 3Ј,5Ј-ADP binds with the 5Ј-phosphate group in P 1 and the adenosine in the B 2 pocket. Two different binding modes are observed in the two RNase A molecules of the asymmetric unit for 2Ј,5Ј-ADP. This inhibitor binds with either the 3Ј or the 5Ј phosphate groups in subsite P 1 , and in each case, the adenosine binds in two different positions within the B 2 subsite. The two uridilyl inhibitors bind similarly with the uridine moiety in the B 1 subsite but the placement of a different phosphate group in P 1 (2Ј versus 3Ј) has significant implications on their potency against RNase A. Comparative structural analysis of the RNase A, eosinophil-derived neurotoxin (EDN), eosinophil cationic protein (ECP), and human angiogenin (Ang) complexes with these and other phosphonucleotide inhibitors provides a wealth of information for structurebased design of inhibitors specific for each RNase. These inhibitors could be developed to therapeutic agents that could control the biological activities of EDN, ECP, and ANG, which play key roles in human pathologies.

No abstract

No abstract

Ssn6, a yeast protein that comprises 10 tandem tetratricopeptide repeat (TPR) motifs, associates with Tup1 repressor protein and acts as a transcriptional corepressor. In this report we identify point mutations in the TPR1 of Ssn6 that disrupt Tup1 interaction. Furthermore, we construct a 3D model of the TPR domain of Ssn6, which is responsible for Tup1 binding, based on the known structure of protein phosphatase 5. According to this model all selected mutations reduce the ability of Ssn6 to interact with Tup1 by affecting the structural integrity of TPR1 and/or the correct spatial arrangement of TPR1 relative to TPR2 and TPR3.z 2000 Federation of European Biochemical Societies.